Conventionally, pre-crash safety (PCS) systems are known; these PCS systems mitigate and/or avoid collision damages between an own vehicle and objects, i.e. obstacles, such as other vehicles, pedestrians, or road structures located in the travelling direction of the own vehicle. Such a PCS system obtains a time to collision (TTC) with an object based on a relative distance of the obstacle with respect to the own vehicle and a relative speed or a relative acceleration of the obstacle relative to the own vehicle. The TTC represents a margin time until which the own vehicle would collide with the obstacle. Then, the PCS system causes a warning device to provide, to the driver of the own vehicle, a warning about the approach of the obstacle, and/or activates a braking device of the own vehicle.
As an example of such a PCS system, a cruise-assist system is disclosed in patent document 1. The cruise-assist system disclosed in patent document 1 sets a risk level indicative of a risk of collision between an own vehicle and an object, and provides, to a driver, drive-assist information based on the risk level.